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Physico-chemical characteristicsFire resistance

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FIRERESISTANCE

The fire performance of most construction materials is a fundamental requisite in

the C Є marking.

According to European Commission decision 96/603/EC, all ceramic tiles that

have received no organic treatment are classified, without any need for testing, in class

A1 of reaction to fire. As a result, the following codes appear in the C Є marking :

►

A1 in ceramic tiles intended for wall tiling

►

A1fl in ceramic tiles intended for flooring

Ceramic tiles which, after the manufacturing process, have received a treatment

that involves the presence of organic matter in a percentage exceeding 1% (for example,

in protection primers for terracotta or fired clay tiles, or in anti-slip treatments applied

on to porcelain tile or glazed stoneware tile), shall display the following codes in the C Є

marking :

►

F in tiles intended for wall tiling

► Ffl in tiles intended for flooring

To be noted are the excellent properties of ceramic tile with respect to fire and

fire propagation. The ceramic cladding of a construction element does not burn or produce toxic combustion gases; in addition, it inhibits fire propagation and, for a

certain time, slows down heat propagation.

Fire resistance according to EN 13501-1

This wide-ranging standard, published in February 2002, sets out in its first part

the classification of materials, with their corresponding codes, based on the data

obtained in the fire reaction tests. It includes the definition of terms and symbols, test

methods, principles for test and sample preparation, testing of materials depending on

whether they are applied to floors or not, criteria, and presentation of the classification.

The test methods envisaged in the standard include the following:

► Non-combustibility test (according to prEN ISO 1182) to identify materials

that will not contribute to fire propagation, or that will do so in a negligible

way. This is a pertinent test for classes A1, A2, A1 fl, and A2fl.

►

Test for the determination of the heat of combustion (according to prEN ISO

1716), which determines the maximum heat given off by a product when it

burns completely, independently of its final use. This is appropriate for the

same classes as the foregoing test.

► Single burning item test (according to EN 13823), which evaluates the

potential contribution of a product to the development of a fire, under a firesituation that simulates a single burning item in a corner of a room near that

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product. It shall be applied for classes A2, B, C, and D; also for class A1 in

certain cases.

►

Ignitability test (according to prEN ISO 11925-2), which evaluates the

ignitability of a product exposed to a small flame. It is applied to classes B,C, D, E, Bfl, Cfl, Dfl, and Efl.

►

Reaction to fire tests for floor coverings. Determination of the burning

behaviour of floor coverings using a radiant heat source (according to prEN

ISO 9239-1), which determines the critical radiant flux below which flames

are not propagated on a horizontal surface. This is used to assign classes

A2fl, Bfl, Cfl, and Dfl.

The standard includes individual tables that set out the classes, the requirements

for each class, as well as additional classifications in certain parameters, and the test

methods applied to evaluate those requirements. The classification and codes are

applied to all types of building materials, excluding those intended for floor coverings(Table 1), and those intended for floor coverings (Table 2). A qualitative description of

the different codes is provided below.

The second part of the standard (UNE-EN 13501-2) is devoted to the

characterisation and classification of construction elements in relation to their fire

performance, based on the fire resistance test, which will be applicable to modular

rigid coverings that adopt protective functions for load-bearing elements or act as

separation membranes.

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CLASSIFICATION OF CONSTRUCTION MATERIALS, EXCEPT THOSE INTENDED FOR FLOOR

COVERINGS, ACCORDING TO THEIR REACTION TO FIRE (UNE-EN 13501-1)

Class Description

F Products for which reaction-to-fire performance has not been determined or which cannot beclassified as A1, A2, B, C, D or E.

E Products capable of resisting, for a short time, small-flame attack without substantial flame propagation taking place.

D Products that satisfy the criteria corresponding to class E and that are able to resist, for alonger time, small-flame attack without any substantial flame propagation taking place. In

addition, they shall also be able to withstand thermal attack by a single burning item withsufficient delay, while giving off limited heat.

C Like class D, but satisfying more stringent requirements. In addition, under thermal attack bya single burning item they shall provide lateral propagation of the limited flame.

B Like class C, but satisfying more stringent requirements.

A2 They must such satisfy the same criteria as class B according to standard EN 13823. In

addition, under conditions of fully developed fire, these products shall not contribute in anyimportant way to fire loading and fire growth.

A1 The products of class A1 shall not contribute to any phase of the fire including the onecorresponding to the fully developed fire. For this reason, it is assumed that they are able

automatically to satisfy all requirements of all the lower classes.

Additional classification according to smoke production

s3 No limitation of smoke production is required.

s2 Total smoke production, as well as the rate of increasing smoke production, is limited.

s1 Stricter criteria are satisfied than those of class s2.

Additional classification according to the production of drops/particles

d2 There are no limitations.

d1 No burning droplets/particles persisting beyond a given time are produced.

d0 No burning droplets/particles are produced.

Table 1

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CLASSIFICATION OF CONSTRUCTION MATERIALS INTENDED FOR FLOOR COVERINGS, ACCORDING

TO UNE-EN 13501-1

Class Description

Ffl Products for which reaction-to-fire performance has not been determined or which cannot beclassified as A1fl, A2fl, Bfl, Cfl, Dfl, or Efl.

Efl Products capable of resisting small-flame attack.

Dfl Products that satisfy class Efl requirements and that are also able to resist, for a given time,

attack by heat flux.

Cfl Like class Dfl, but satisfying more stringent requirements.

Bfl Like class Cfl, but satisfying more stringent requirements.

A2fl Products that such satisfy the same requirements as class Bfl in relation to heat flux. Inaddition, under conditions of fully developed fire, these products shall not contribute in any

important way to fire loading and fire growth.

A1fl The products of class A1fl shall not contribute to any phase of the fire including the onecorresponding to the fully developed fire. For this reason, it is assumed that they are ableautomatically to satisfy all requirements of all the lower classes.

Additional classification according to smoke production

s2 There is no limitation.

s1 Total smoke production is limited.

Table 2

Scientific-technical aspects of heat, flames, and their propagation in a fire

In order to understand the relative importance of the nature of the construction

elements in relation to the development and consequences of a fire, it would be

interesting to establish the general phases in which this phenomenon takes place.

Thus, if temperature is plotted as a function of fire development in a diagram,

three different phases may be distinguished:

• An initial or ignition phase in which temperature increases slowly, since

most of the heat is used in generating combustion and in evaporating the

water contained in the materials.

• An intermediate phase in which temperature increases very quickly up to

800–900 ºC, as a result of heat build-up, flame irradiation, and the greater

quantity of combustible material involved.

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• A final extinction phase in which heat loss through the walls, the effect of

smoke, lack of oxygen, and air entry exceed the combustion heat.

Certain studies aimed at analysing materials and the parameters that define how

these materials behave in relation to fire have been conducted(1)

. Thus, the followingmay be distinguished:

Material constituents of load-bearing structures

Reinforced concrete has always been considered a safe material in

relation to fire. However, the improved mechanical properties of cementing

agents and steel, as well as the increased use of pre-compression treatments and

prefabrication have led to lighter structures with a smaller cross-section, which

display the same mechanical performance features.

In the case of fire, these structures reach more quickly the criticaltemperature at which their mechanical performance decreases. For that reason,

with a view to avoiding or preventing the risk of structural failure, legislation on

materials envisages different measures in regard to the coverings of load-bearing

structures (use of insulation such as gypsum and vermiculite, renderings of

different thickness, etc.).

Material constituents of non-load-bearing structures

The fire performance of flooring and wall cladding materials (including

ceramic tiles) may be evaluated on the basis of the following parameters:

1. Heating power: Defined as the quantity of heat developed in the

burn-up of a substance. According to this parameter, ceramic floor

and wall tilings display complete inertia to combustion, in the range

of temperatures that usually occur in a fire.

2. Oxygen index: This is the minimum required oxygen concentration

to keep a material burning. Ceramic materials are fireproof at any

oxygen concentration.

3. Ignition or spontaneous combustion temperature: These are

temperatures at which a material starts to burn in the presence or

absence of a flame, respectively. Once again, ceramic materials arefireproof.

4. Development of the flame: This corresponds to the rate of advance

of the flame front.

5. Flammability: This is defined as the rate at which the flame travels

from one side of the material to the other.

6. Length of the flames.

7. Combustibility: Parameter that considers the heat produced by

combustion of the material and the speed at which this takes place.

(1)

Behaviour of building materials in a fire. C. PALMONARI AND F. VAUGHAN.

CEC, European Ceramic Tile Manufacturers’ Federation. Published in 1979.

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In regard to these last four parameters, ceramic floor and wall tiles are

also completely inert to combustion.

8. Density and toxicity of smoke: Many materials used in non-load-

bearing structures produce smoke emissions. Smoke density is

measured according to the standard of the National Bureau of

Standards. Smoke is hazardous in itself, since it reduces visibility,

hindering possible escape from a building in flames. However, in

addition, it entails a risk of asphyxia and poisoning, since carbon

monoxide is present in larger or smaller quantities in all combustion

smoke. On the other hand, the use of organic materials of a

petrochemical nature (PVC, polyurethane foams, and acrylic fibres)

leads to increased concentrations of hydrocyanic acid and other toxic

substances.

Ceramic floor and wall tiles produce

absolutely no toxic smoke or gas emissions,

which is why they are the most appropriate

materials – together with their positive

response in the other parameters for use in

housing, and public buildings frequented by

many people, such as hotels, offices,

hospitals, service and commercial areas,

theatres, etc.


6

The enclosed figures present some of

the results mentioned in the foregoing

paragraphs.

A factor that needs to be taken into

account, when it comes to evaluating

ceramic tiling performance in relation to fire,

is the fire response of the bonding and

grouting materials used in tile fixing.

The tests conducted by the Rubber

and Plastic Research Association of Great

Britain, Shawbury, on panels of ceramic tiles

installed with different materials, led to the

following results:

Production of smoke and toxic gases

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• Solvent-based adhesives are hazardous in tile installation owing to their risk

of flammability and toxicity; however, once the solvents have evaporated

they are safe adhesives even under extreme conditions (flame in direct

contact with the tile and glazed surface temperature of 535 ºC), and do notcatch fire or lose their bonding properties.

• Polyvinyl acetate adhesives display no alterations at a surface temperature of

350 ºC. At higher temperatures they exhibit adhesion loss, though they

remain fireproof.

• Latex adhesives are least resistant to fire, displaying considerable adhesion

loss at 350 ºC and emitting non-toxic smoke. Their fire resistance increases

when they are mixed with cement.

• Thin-set cementitious adhesives perform satisfactorily, though breakage

occurs in tiles under the most unfavourable conditions. In thick-set beds, the

results are less satisfactory above 350 ºC.

•

Adhesives made from epoxy resins evidence no alterations below 400 ºC,whereas fracture and detachment phenomena appear at higher temperatures.

In short, it may be concluded that the bonding materials used in ceramic tile

installation display very satisfactory fire performance, demonstrate good mechanical

strength, and produce hardly any emission of fumes or potentially toxic substances.

It may be noted that analysis of laboratory tests and actual experience indicate

that non-load-bearing building structures contribute most to the intensity and spread of

flames, as well as to the formation of smoke and toxic gases. Therefore, appropriate

selection of these materials represents the most effective prevention measure.

In view of the above, it may be concluded that ceramic floor and wall tiles are

the most appropriate preventive coverings in the case of fire, given their

incombustibility, inhibiting capacity for flame propagation, and absolute innocuousness

in relation to the production of smoke and toxic gases. In addition, their delaying action

in fire propagation can be useful for protecting the load-bearing structures, in addition to

the temperature differential that their insulation capacity can establish between the fair

face of the tiling and the base of the structure.

STANDARD HEATING SOURCE

DISTANCE TO THE

CLAD

SURFACE

(IN MM)

TEMPERATURE OF THE

FAIR

FACE OF THE

TILES

(ºC)

TEMPERATURE OF THE BACK

OF THET

ILE(ºC)

152

76

0

350

460

535

80

90

100

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